Uretdione-containing polyurethane-dispersions comprising hydrophilic groups

ABSTRACT

The present invention relates to a specific uretdione prepolymer, and an aqueous curable composition based on the specific uretdione prepolymer. Furthermore, it pertains to a process for curing said aqueous curable composition, the cured article obtained by this process and additionally to the use of said aqueous composition for coatings, adhesives and/or sealants.

The present invention relates to a specific uretdione prepolymer, and anaqueous curable composition based on the specific uretdione prepolymer.Furthermore, it pertains to a process for curing said aqueous curablecomposition, the cured article obtained by this process and additionallyto the use of said aqueous composition for coatings, adhesives and/orsealants.

Aqueous curable compositions based on specific uretdione prepolymers arefor example known from DE 10 2005 036 654 A1. However, thosecompositions do not show a sufficient long-term stability. Thehydrophilization of the polymer is obtained via ionogenic groups.

Therefore, it was an object of the present invention to provide anuretdione prepolymer, which provides an improved aqueous curablecomposition, which shows improved, preferably long-term, storagestability.

It has been surprisingly found by the present inventors that followinguretdione prepolymer can overcome the above-mentioned deficiency:

An uretdione prepolymer, which comprises at least one uretdione group,and which is obtainable by reacting

A1) at least one uretdione polyisocyanate having an isocyanatefunctionality of at least 2.0, whereby said uretdione polyisocyanate isobtained from at least one aliphatic polyisocyanate, with

A2) at least one polyalkoxy ether derivative comprising at least two —OHgroups, which are present on two different non-neighbouring atoms of themolecule and whereby at least one of the —OH groups is not a terminal—OH group, and

A3) at least one reactant, which comprises at least oneZerewitinoff-active group and being different from A2 or which is H₂O,

preferably in the presence of at least one catalyst, to obtain theuretdione prepolymer;

wherein the prepolymer has an acid number of at most 4 mg KOH/g,preferably determined according to DIN EN ISO 2114:2002-06 as 37 wt. %aqueous dispersion.

When the uretdione prepolymer of the present invention is employed inaqueous curable compositions, the thus obtained compositions arehomogenous after storage over a long time, can retain a high amount ofuretdione groups, compared to the initially used ones, the uretdionegroups can be reacted with alcohols or amines, whereby a crosslinking ofthe prepolymers is obtained, the reaction of the uretdione group withalcohol can be catalysed and the cured product obtained by thesecompositions show equivalent or even improved lacquer properties. Not tobe bound by any theory it is assumed that the use of compounds A2 in thepreparation of the prepolymer leads to this properties, since itpromotes chain growth and provides a better cross-linking

In the present invention, any numerical range recited herein is intendedto include all sub-ranges subsumed therein. For example, a range of “1to 10” is intended to include all sub-ranges between (and including) therecited minimum value of 1 and the recited maximum value of 10, that is,having a minimum value equal to or greater than 1 and a maximum value ofequal to or less than 10.

In the present invention, a “monomer” is a low-molecular weight compoundcomprising functional moieties, wherein said monomer functions as abuilding block for polymers and has a defined molecular weight.

In the present invention the term “polymer” refers to a compound, formedduring a chemical reaction by linking several monomers (i.e. more thantwo monomers) of the same or different kind together via covalentbonding, wherein the resulting polymer can differ in its degree ofpolymerization, molecular weight distribution and chain lengthrespectively. Hence, a polymer according to the present invention is acompound, comprising in its molecular structure at least one repeatingunit, which was integrated in the polymer structure during polymersynthesis by repeatedly linking monomers together via covalent bonds toform said polymer structure. The number average molecular weight ispreferably at least 250 g/mol, more preferably at least 1,000 g/mol.

The term “polymer” includes homopolymers, copolymers, block-copolymersand oligomers.

In the present invention, a “prepolymer” is a polymer with reactivegroups. In analogy to the definition of the term “polymer”, themolecular structure of a prepolymer is formed by repeatedly linking morethan two monomers of the same of different kind together. The prepolymercan participate in a subsequent formation of a polymer, which has ahigher molecular weight than said prepolymer. The term “prepolymer”encompasses polymers, which are able to chemically react via at leastone of its reactive groups, forming a repeating unit of a (preferablycrosslinked) polymer. Therefore the term “prepolymer” encompasses aswell self-crosslinking polymers with at least two different kinds ofreactive groups, wherein said groups are able to chemically react amongthemselves, so that the prepolymer molecules are able to crosslink.

According to this invention, if not otherwise specified, the averagemolecular weight is defined as the number average molecular weight Mn.As molecular weight of polymers the number average molecular weight Mnis applied. Mn is determined via gel permeation chromatography (GPC at23° C.) in tetrahydrofurane as the solvent. The measurement is performedas described in DIN 55672-1 (the DIN-version used was at the applicationdate (or priority date if applicable) of the present invention, thelatest version): “Gelpermeationschromatographie, Teil 1—Tetrahydrofuranals Elutionsmittel” (SECurity GPC-System from PSS Polymer Service,flowrate 1.0 ml/min; columns: 2×PSS SDV linear M, 8×300 mm, 5 μm;RID-detector). Samples of polystyrene standards of known molecularweight were used for calibration. The calculation of the number averagemolecular weight was performed by software. Baseline values andevaluation threshold values were determined according to abovereferenced DIN 55672 Teil 1.

The term “low-molecular” is defined to encompass a molecular weight upto 800 g/mol.

The term “high-molecular” is defined to encompass a molecular weightabove 800 g/mol.

An “organic compound” contains at least one moiety, comprising acarbon-hydrogen covalent bond.

According to this application the term “aliphatic” is defined asnon-aromatic hydrocarbyl groups being saturated or unsaturated.

According to this application the term “araliphatic” is defined ashydrocarbyl moieties composed of a non-aromatic, as well as saturated orunsaturated hydrocarbyl group, which is directly bonded to an aromaticmoiety.

According to this application the term “alicyclic” or “cycloaliphatic”are optionally substituted, carbocyclic or heterocyclic compounds ormoieties, which are non-aromatic (like for example cycloalkanes,cycloalkenes or oxa-, thia-, aza- or thiazacycloalkanes). Particularexamples are cyclohexyl groups, cyclopentyl groups, and their N- orO-heterocyclic derivatives like for example pyrimidine, pyrazine,tetrahydropyrane or tetrahydrofurane.

In case the groups or compounds are disclosed to be “optionallysubstituted” or “substituted”, suitable substituents are —F, —Cl, —I,—Br, —OH, —OCH₃, —OCH₂CH₃, —O-Isopropyl or —O-nPropyl, —OCF₃, —CF₃,—S—C₁₋₆-Alkyl and/or (optionally via a hetero atom attached) a linear orbranched, aliphatic and/or alicyclic structural unit with 1 to 12 carbonatoms, respectively functioning as a substitute for a carbon boundhydrogen atom of the molecule in question. Preferred substituents arehalogen (especially —F, —Cl), C₁₋₆-Alkoxy (especially methoxy andethoxy), hydroxy, trifluoromethyl and trifluoromethoxy, respectivelyfunctioning as a substitute for a carbon bound hydrogen atom of themolecule in question.

In a formula illustrating the structure of a chemical moiety, a covalentbond of said formula marked with a * defines the covalent bond, whichconnects said illustrated moiety to the rest of a more complex molecularstructure.

The term “transparent” preferably means that the coating (with athickness of 45 μm) is capable of transmitting rays of visible light sobodies situated beyond or behind can be distinctly seen. Transparentcoatings according to this invention exhibit a Haze-value<20 (Hazemeasurement instrument: DIN EN ISO 2813 (the DIN-version used at theapplication date (or at the priority date if applicable) of the presentinvention at the latest version).

The present invention in particular pertains to:

-   1. An uretdione prepolymer, which comprises at least one uretdione    group, and which is obtainable by reacting    -   A1) at least one uretdione polyisocyanate having an isocyanate        functionality of at least 2.0, whereby said uretdione        polyisocyanate is obtained from at least one aliphatic        polyisocyanate, with    -   A2) at least one polyalkoxy ether derivative comprising at least        two —OH groups, which are present on two different        non-neighbouring atoms of the molecule and whereby at least one        of the —OH groups is not a terminal —OH group, and    -   A3) at least one reactant, which comprises at least one        Zerewitinoff-active group and being different from A2 or which        is H₂O,    -   preferably in the presence of at least one catalyst, to obtain        the uretdione prepolymer;    -   wherein the prepolymer has an acid number of at most 4 mg KOH/g,        preferably determined according to DIN EN ISO 2114:2002-06 as 37        wt. % aqueous dispersion.-   2. The uretdione prepolymer according to aspect 1, characterized in    that    -   in a first step, the at least one uretdione polyisocyanate A1 is        reacted, preferably in the presence of a catalyst, with the at        least one polyalkoxy ether derivative A2, wherein after the        first step the resulting intermediate product has preferably an        isocyanate content of 0.5 to 10 wt.-%, preferably 1 to 6 wt.-%,        more preferably 2 to 4 wt.-%, measured according to DIN EN ISO        11909:2007-05;    -   and in a second step the polymer obtained in the first step is        reacted with the at least one reactant A3.-   3. The uretdione prepolymer according to aspect 1, characterized in    that the components A1 to A3 are reacted in a one-step process,    preferably in the presence of a catalyst.-   4. The uretdione prepolymer according to aspect 1, characterized in    that    -   in a first step, the at least one uretdione polyisocyanate A1 is        reacted with the at least one reactant A3 and in a second step        the polymer obtained in the first step is reacted in a second        step with the at least one polyalkoxy ether derivative A2,        preferably in the presence of a catalyst.-   5. The uretdione prepolymer according to any one of the above    aspects, characterized in that said uretdione prepolymer is a    nonionic prepolymer.-   6. The uretdione prepolymer according to any one of the above    aspects, characterized in that said uretdione prepolymer exhibits a    zeta potential of at least −20 mV.-   7. The uretdione prepolymer according to any one of the above    aspects, characterized in that said uretdione prepolymer comprises    at least one *—O—(CH₂CH₂O)_(n)—R moiety, in which R is a hydrogen    atom or a (C₁-C₄)-alkyl group and n is a number from 3 to 100.-   8. The uretdione prepolymer according to any one of the above    aspects, characterized in that said uretdione polyisocyanate A1 is    obtained from at least one cycloaliphatic polyisocyanate.-   9. The uretdione prepolymer according to any one of the above    aspects, characterized in that said uretdione polyisocyanate A1 is    obtained from isophorone diisocyanate (IPDI), 1,6-diisocyanatohexane    (HDI) or mixtures thereof.-   10. The uretdione prepolymer according to any one of the above    aspects, characterized in that said uretdione polyisocyanate A1 is    prepared from at least 20 mol % isophorone diisocyanate (IPDI) based    on the total amount of polyisocyanates used.-   11. The uretdione prepolymer according to any one of the above    aspects, characterized in that said uretdione polyisocyanate A1 is    prepared from isophorone diisocyanate as the only polyisocyanate    used.-   12. The uretdione prepolymer according to any one of the above    aspects, characterized in that the uretdione polyisocyanate A1    contains from 1 to 10 uretdione moieties.-   13. The uretdione prepolymer according to any one of the above    aspects, characterized in that compound A2 is selected from    compounds of formula (I):

-   -   characterized in that    -   X is H or alkyl, preferably H or C₁₋₂₀-alkyl, more preferably H        or C₂₋₁₀-alkyl;    -   R is a C₁₋₄ alkylene group;    -   p is an integer of 2 to 50;    -   in each unit p    -   n is independently 0 or 1 and    -   m is independently 0 or 1,    -   with the proviso that at least one of n or m in each unit p is        1;    -   preferably characterized in that    -   X is H, methyl, ethyl, or propyl, preferably ethyl;    -   R is methyl;    -   is an integer of 5 to 25;    -   in each unit p    -   n is independently 0 or 1 and    -   m is independently 0 or 1,    -   with the proviso that at least one of n or m in each unit p is 1        and the total amount of n≥m, preferably the total amount of n is        at least 2*m, more preferably n is at least 3*m, most preferably        only n is present.

-   14. The uretdione prepolymer according to any one of the above    aspects, characterized in that compounds A3 is selected from at    least one polyol which is different from A2, preferably selected    from polyester polyols, polyether polyols, polyurethane polyols,    polyacrylate polyols, polymethacrylate polyols, polycarbonate    polyols or mixtures thereof, preferably A3 is selected from    polyester polyols, polyether polyols, polycarbonate polyols,    polyurethane polyols, polyacrylate polyols, polymethacrylate    polyols, C₂-C₁₀-hydrocarbons with at least two hydroxyl groups, or    mixtures thereof, most preferably A3 is a polyester polyol.

-   15. The uretdione prepolymer according to any one of the above    aspects, characterized in that said compound A1 is used in an amount    of 3.0 to 50.0 wt. % based on the total weight of compounds A1 to    A3.

-   16. The uretdione prepolymer according to any one of the above    aspects, characterized in that said compound A2 is used in amount of    50 to 97 wt.-% based on the total weight of compounds A1 to A3.

-   17. The uretdione prepolymer according to any one of the above    aspects, characterized in that the weight ratio of A1 to A2 is from    1:1 to 1:32.3.

-   18. An aqueous, curable composition, comprising or consisting of    -   the uretdione prepolymer according to any one of aspects 1 to        17, and    -   optionally at least one compound, which comprises at least one        Zerewitinoff-active group and/or    -   optionally at least one azolate-compound.

-   19. The aqueous, curable composition according to aspect 18,    characterized in that said uretdione prepolymer is a dispersed    uretdione prepolymer, preferably characterized in that the uretdione    prepolymer is suspended in the aqueous liquid.

-   20. The aqueous, curable composition according to aspect 18 or 19,    characterized in that said uretdione prepolymer is contained in a    total amount of 3 to 40 wt. % based on the total weight of the    composition.

-   21. The aqueous, curable composition according to any one of aspects    18 to 20, characterized in that said composition is substantially    free of compounds comprising at least one isocyanate moiety.

-   22. The aqueous, curable composition according to any one of aspects    18 to 21, characterized in that said azolate-compound is selected    from at least one triazolate-compound of formula (III) or salts    thereof and formula (IV) or salts thereof

-   -   characterized in that    -   R¹, R², R³ and R⁴ are independently selected from a hydrogen        atom, a halogen atom, a nitro group, a saturated or unsaturated,        aliphatic or cycloaliphatic radical, an optionally substituted        aromatic group comprising up to 20 carbon atoms and optionally        up to 3 heteroatoms selected from oxygen, sulphur, nitrogen, an        optionally substituted araliphatic group comprising up to 20        carbon atoms and optionally up to 3 heteroatoms selected from        oxygen, sulphur, nitrogen, and whereby R³ and R⁴ of formula (IV)        together with the carbon atoms of the 1,2,3-triazolate        five-membered ring form fused rings with 3 to 6 carbon atoms.

-   23. The aqueous, curable composition according to aspect 22,    characterized in that said azolate-compound is selected from    alkaline metal-1,2,4-triazolate, alkaline metal-1,2,3-triazolate,    alkaline metal-benzotriazolate, alkaline earth    metal-1,2,4-triazolate, alkaline earth metal-1,2,3-triazolate,    alkaline earth metal-benzotriazolate.

-   24. The aqueous, curable composition according to any one of aspects    18 to 23, characterized in that said at least one compound, which    comprises at least one Zerewitinoff-active group is selected from    polyester polyols, polyether polyols, polyurethane polyols,    polyacrylate polyols, polymethacrylate polyols, or polycarbonate    polyols and mixtures thereof.

-   25. The aqueous, curable composition according to any one of aspects    18 to 24, characterized in that said uretdione prepolymer is    contained in an amount of 1 to 50 wt. % and/or    -   said at least one compound, which comprises at least one        Zerewitinoff-active group is contained in an amount of 0 to 80        wt.-% and/or    -   said triazolate-compound is contained in an amount of 0.1 to 10        wt. %, based on the total weight of the composition,        respectively.

-   26. The aqueous, curable composition according to any one of aspects    18 to 25, characterized in that the composition comprises water in    an amount of 10 to 85 wt. %, based on the total weight of the    composition.

-   27. The aqueous, curable composition according to any one of aspects    18 to 26, characterized in that the pH-value at 20° C. is from pH 5    to pH 13.

-   28. Process for curing a liquid composition on a substrate,    comprising    -   a) applying on a substrate an aqueous, curable composition        according to any one of aspects 18 to 27; and    -   a) exposing the deposited aqueous, curable composition to a        temperature of 60° C. to 160° C. to cure said deposited curing        composition.

-   29. A cured article obtainable by the process according to aspect    28.

-   30. Use of the composition according to any one of aspects 18 to 27    for coatings, adhesives and/or sealants.

Suitable uretdione polyisocyanates A1 are typically obtained bycatalytic dimerization of polyisocyanates by methods which are known inthe art. Examples of suitable polyisocyanates include diisocyanates suchas linear aliphatic polyisocyanates, cycloaliphatic polyisocyanates andalkaryl polyisocyanates. Specific examples include1,4-diisocyanatobutane, 1,5-diisocyanatopentane (PDI),1,6-diisocyanatohexane (HDI), 2,4′- and/or4,4′-diisocyanatocyclohexylmethane (HMDI), isophorone diisocyanate(IPDI), 1,3- and 1,4-bisisocyanatomethylcyclohexane, 1,3- and1,4-xylylene diisocyanates (XDI) and mixtures thereof.

Examples of dimerization catalysts are: trialkylphosphines,aminophosphines and aminopyridines such as dimethylaminopyridines, andtris(dimethylamino)phosphine, as well as any other dimerization catalystknown to those skilled in the art. The result of the dimerizationreaction depends, in a manner known to the skilled person, on thecatalyst used, on the process conditions and on the polyisocyanatesemployed. In particular it is possible for products to be formed whichcontain on average more than one uretdione group per molecule, thenumber of uretdione groups being subject to a distribution.

The uretdione polyisocyanate A1 preferably on average contains from 1 to10 uretdione moieties.

Preferably said uretdione polyisocyanate A1 is prepared from at leastone cycloaliphatic polyisocyanate. In another preferred embodiment, saiduretdione polyisocyanate A1 is prepared from at least 20 mol %isophorone diisocyanate (IPDI) based on the total amount ofpolyisocyanates used. Said uretdione polyisocyanate A1 is most preferredprepared from isophorone diisocyanate as the only polyisocyanate used.Alternatively the uretdione polyisocyanate A1 is preferably preparedfrom isophorone diisocyanate (IPDI), 1,6-diisocyanatohexane (HDI) ormixtures thereof.

Preferred uretdione polyisocyanates are for example commerciallyavailable as Desmodur N3400 from Covestro Deutschland AG, Leverkusen,Germany.

Component A2 is at least one polyalkoxy ether derivative comprising atleast two —OH groups, which are present on two differentnon-neighbouring atoms of the molecule and whereby at least one of the—OH groups is not a terminal —OH group. Preferred embodiments aredefined in formula (I) above.

Preferred commercially available examples are Ymer™ N120 (CAS number:131483-27-7) by Perstorp Holding AB, Malmö, Sweden and Tegomer® D 3403(Evonik Industries AG, Essen, DE).

Component A3 is at least one reactant, which comprises at least oneZerewitinoff-active group and being different from A2 or H₂O; preferablyat least one Zerewitinoff-active group and being different from A2.

A “Zerewitinoff-active group” is defined as a functional group,comprising at least one Zerewitinoff-active hydrogen atom, being anacidic hydrogen atom or active hydrogen atom. The abundance of such anactive hydrogen atom is determined by a known reaction of the compoundin question with a Grignard reagent. The amount of Zerewitinoff-activehydrogen atoms is typically determined by measuring the amount ofreleased methane gas, and subsequently calculated in consideration ofthe stoichiometry of the following reaction equation, wherein for eachmole of active hydrogen atoms of the compound in question (R—XH) onemole of methyl magnesium bromide (CH₃—MgBr) is used and one mole ofmethane is released:

CH₃—MgBr+R—XH→CH₄+MG (XR)Br

Zerewitinoff-active groups are in particular C—H active organic groups,—OH, —SH, —NH₂ or —NHR′ wherein R′ denotes an organic moiety. PreferablyZerewitinoff-active groups are selected from —OH, —SH, —NH₂ or —NHR′wherein R′ denotes an organic moiety. Especially preferred, theZerewitinoff-active groups according to the invention are —OH. Aparticularly preferred uretdione prepolymer as component A+B) comprisesas Zerewitinoff-active groups at least two hydroxy groups.

It was also found, that the curing time was improved by introducinghydrophilic groups as grafts or terminus into the structure of saiduretdione prepolymer. It is preferred, when said hydrophilic groups donot comprise an ionic moiety. A preferred uretdione prepolymer comprisesgrafts with at least one hydrophilic group selected from polyoxyalkyleneether capped with methyl, ethyl, propyl or butyl, polyethyleneoxidecapped with one methyl group, Polyethyleneoxide capped with one ethyl,propyl, or butyl group. Particularly preferred uretdione prepolymerscomprise additionally on average at least one *—O—(CH₂CH₂O)_(n)—Rmoiety, in which R denotes a (C₁-C₄)-alkyl group and n denotes a numberfrom 3 to 100. n denotes preferably a number from 5 to 70, morepreferably from 7 to 55. R is preferably a methyl group.

Said hydrophilic groups are introduced into the structure of saiduretdione prepolymer by (preferably nonionic) hydrophilizing agents.Suitable nonionically hydrophilizing agents are, for example,polyoxyalkylene ethers which have isocyanate-reactive groups, such ashydroxy, amino or thiol groups. A preference is given tomonohydroxy-functional polyalkylene oxide polyether alcohols having, onstatistical average, 5 to 70, preferably 7 to 55, ethylene oxide unitsper molecule, as are accessible in a manner known per se by alkoxylationof suitable starter molecules (e.g. in Ullmanns Encyclopädie dertechnischen Chemie [Ullmanns encyclopaedia of industrial chemistry], 4thedition, Volume 19, Verlag Chemie, Weinheim pp. 31-38). These are eitherpure polyethylene oxide ethers or mixed polyalkylene oxide ethers, wherethey contain at least 30 mol %, preferably at least 40 mol %, ethyleneoxide units, based on all of the alkylene oxide units present.

Suitable starter molecules for such nonionic hydrophilizing agents arein particular saturated monoalcohols, such as methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, theisomeric pentanols, hexanols, octanols and nonanols, n-decanol,n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol,the isomeric methylcyclohexanols or hydroxymethylcyclohexane,3-ethyl-3-hydroxymethyloxetane or tetrahydrofurfuryl alcohol, diethyleneglycol monoalkyl ethers, such as, for example, diethylene glycolmonobutyl ether, unsaturated alcohols, such as allyl alcohol,1,1-dimethylallyl alcohol or oleyl alcohol, aromatic alcohols, such asphenol, the isomeric cresols or methoxyphenols, araliphatic alcohols,such as benzyl alcohol, anisyl alcohol or cinnamyl alcohol, secondarymonoamines, such as dimethylamine, diethylamine, dipropylamine,diisopropylamine, dibutylamine, bis(2-ethylhexyl)amine, N-methyl- andN-ethylcyclohexylamine or dicyclohexylamine, and also heterocyclicsecondary amines, such as morpholine, pyrrolidine, piperidine or1H-pyrazole. Preferred starter molecules are saturated monoalcohols ofthe type specified above. Particular preference is given to usingdiethylene glycol monobutyl ether or n-butanol as starter molecules.

Alkylene oxides suitable for the alkoxylation reaction are in particularethylene oxide and propylene oxide, which can be used in thealkoxylation reaction in any desired order or else in a mixture.

Particularly preferred nonionic hydrophilizing agents are monofunctionalmixed polyalkylene oxide polyethers, which have 40 to 100 mol % ethyleneoxide units and 0 to 60 mol % propylene oxide units.

Suitable polyol as compound A3 is preferred selected from polyesterpolyol, polyether polyol, polyurethane polyol, polycarbonate polyol,polyacrylate polyol, polymethacrylate polyol, C₂-C₁₀-hydrocarbon with atleast two hydroxyl groups, or mixtures thereof.

The term “polyol” includes materials having an average of two or moreprimary hydroxyl groups per molecule. The polyols useful in the practicecan be either low or high molecular weight materials and in general willhave average hydroxyl values as determined by ASTM designation E-222-67,Method B, between about 1000 and 2, and preferably between about 500 and2. The polyols include low molecular weight diols, triols and higheralcohols and polymeric polyols such as polyester polyols, polyetherpolyols, polyurethane polyols and hydroxy-containing (meth)acrylicpolymers.

The low molecular weight diols, triols and higher alcohols useful in theinstant invention are known in the art. For the most part they aremonomeric and have hydroxy values of 200 and above, usually within therange of 1500 to 200. Such materials include aliphatic polyols,particularly alkylene polyols containing from 2 to 18 carbon atoms.Examples include ethylene glycol, 1,4-butanediol, 1,6-hexanediol;cycloaliphatic polyols such as cyclohexane dimethanol. Examples oftriols and higher alcohols include trimethylol propane andpentaerythritol. Also useful are polyols containing either linkages suchas diethylene glycol and triethylene glycol.

The most suitable polymeric polyols are those having hydroxyl valuesless than 200, such as 10 to 180. Examples of polymeric polyols includepolyalkylene ether polyols, polyester polyols includinghydroxyl-containing polycaprolactones, hydroxy-containing (meth)acrylicpolymers, polycarbonate polyols and polyurethane polyols.

Examples of polyether polyols are poly(oxytetramethylene) glycols,poly(oxyethylene) glycols, poly(oxypropylene) glycols, and the reactionproduct of ethylene glycol with a mixture of propylene oxide andethylene oxide.

Also useful are polyether polyols formed from the oxyalkylation ofvarious polyols, for example, glycols such as ethylene glycol,1,4-butane glycol, 1,6-hexanediol, and the like, or higher polyols, suchas trimethylol propane, pentaerythritol and the like. One commonlyutilized oxyalkylation method is by reacting a polyol with an alkyleneoxide, for example, ethylene oxide in the presence of an acidic or basiccatalyst.

Polyester polyols can also be used as a polymeric polyol component inthe practice of the invention. The polyester polyols can be prepared bythe polyesterification of organic polycarboxylic acids or anhydridesthereof with organic polyols. Usually, the polycarboxylic acids andpolyols are aliphatic or aromatic dibasic acids and diols.

The diols which are usually employed in making the polyester includealkylene glycols, such as ethylene glycol and butylene glycol, neopentylglycol and other glycols such as cyclohexane dimethanol, caprolactonediol (for example, the reaction product of caprolactone and ethyleneglycol), polyether glycols, for example, poly(oxytetramethylene) glycoland the like. However, other diols of various types and, as indicated,polyols of higher functionality can also be utilized. Such higherpolyols preferably include, for example, trimethylol propane,trimethylol ethane, pentaerythritol, and the like, as well as highermolecular weight polyols such as those produced by oxyalkylating lowmolecular weight polyols. A particularly preferred example of such highmolecular weight polyol is the reaction product of 20 moles of ethyleneoxide per mole of trimethylol propane.

The acid component of the polyester polyols consists primarily ofmonomeric carboxylic acids or anhydrides having 2 to 18 carbon atoms permolecule. Among the acids which are useful are phthalic acid,isophthalic acid, terephthalic acid, tetrahydrophthalic acid,hexahydrophthalic acid, adipic acid, azelaic acid, sebacic acid, maleicacid, glutaric acid, chlorendic acid, tetrachlorophthalic acid and otherdicarboxylic acids of varying types. Also, there may be employed higherpolycarboxylic acids such as trimellitic acid and tricarballylic acid(where acids are referred to above, it is understood that the anhydridesof those acids which form anhydrides can be used in place of the acid).Also, lower alkyl esters of acids such as dimethyl glutarate can beused.

Besides polyester polyols formed from polybasic acids and polyols,polycaprolactone-type polyesters can also be employed. These productsare formed from the reaction of a cyclic lactone such asepsilon-caprolactone with a polyol with primary hydroxyls such as thosementioned above. Such products are described in U.S. Pat. No. 3,169,945to Hostettler.

In addition to the polyether polyols and polyester polyols,hydroxy-containing (meth)acrylic polymers or (meth)acrylic polyols canbe used as the polyol component.

Among the (meth)acrylic polymers are polymers of about 2 to 20 percentby weight primary hydroxy-containing vinyl monomers such as hydroxyalkylacrylate and methacrylate having 2 to 6 carbon atoms in the alkyl groupand 80 to 98 percent by weight of other ethylenically unsaturatedcopolymerizable materials such as alkyl (meth)acrylates; the percentagesby weight being based on the total weight of the monomeric charge.

Examples of suitable hydroxy alkyl (meth)acrylates are hydroxyl ethyland hydroxy butyl (meth)acrylate. Examples of suitable alkyl acrylatesand (meth)acrylates are lauryl methacrylate, 2-ethylhexyl methacrylateand n-butyl acrylate.

Besides the acrylates and methacrylates, other copolymerizable monomerswhich can be copolymerized with the hydroxyalkyl (meth)acrylates areethylenically unsaturated materials such as monoolefinic and diolefinichydrocarbons, halogenated monoolefinic and diolefinic hydrocarbons,unsaturated esters of organic and inorganic acids, amides and esters ofunsaturated acids, nitriles and unsaturated acids and the like. Examplesof such monomers include styrene, 1,3-butadiene, acrylamide,acrylonitrile, alpha-methyl styrene, alpha-methyl chlorostyrene, vinylbutyrate, vinyl acetate, alkyl chloride, divinyl benzene, diallylitaconate, triallyl cyanurate and mixtures thereof. Usually these otherethylenically unsaturated materials are used in admixture with theabove-mentioned acrylates and methacrylates.

The mean weight average molecular weight M_(w) of the uretdioneprepolymer, measured with GPC as described above, but withN,N-dimethylacetamide instead of tetrahydrofurane as solvent andcalculated as M_(w) is preferably in the range of 20,000 to 800,000g/mol, particular preferred in the range of 100,000 to 500,000 g/mol.

The uretdione prepolymer exhibits an acid number of at most 4 mg KOH/g,preferably at most 3.5 mg KOH/g, particularly preferably 3.0 mg KOH/g,most preferably at most 2.5 mg KOH/g (each determined according to DINEN ISO 2114:2002-06). This significantly reduces the curing time of theaqueous composition. The acid number is measured according to DIN EN ISO2114:2002-06. The sample for determining the acid number essentiallyconsists (or consists) of 37 wt. % uretdione prepolymer and water andinstead of a mixture of toluene and ethanol as described in DIN EN ISO2114:2002-06, a mixture of acetone and ethanol in a weight ratio of 2:1was used.

The uretdione prepolymer preferably exhibits a zeta potential of −20 mVor higher. The zeta potential of the uretdione prepolymer is preferablydetermined from a dispersion of uretdione prepolymer in water as thesample. One drop of a preformed dispersion of the uretdione prepolymeris highly diluted with 20 ml of demineralized water and homogenized bystirring, leading to the sample. Subsequently the zeta potential isdetermined at 23° C. in the Malvern Nanosizer ZS90 instrument (MalvernInstruments, Herrenberg, Germany). The given values of the zetapotential are always related to said sample of the dispersed uretdionepolymer.

The uretdione prepolymer comprises on average at least one uretdionegroup. It is preferred, that the uretdione prepolymer comprises onaverage at least two uretdione groups. Preferred uretdione prepolymersof this invention are self-curing prepolymers. It is preferred, that theuretdione prepolymer comprises on average at least twoZerewitinoff-active groups. During heat induced curing, the uretdioneprepolymer will (self-)crosslink via reaction of said uretdione groupswith said Zerewitinoff-active groups. The more uretdione groups andZerewitinoff-active groups are on average comprised in said uretdioneprepolymer (or said reactant), the better.

It was found, that it was even possible to cure at low temperatureuretdione prepolymers, which were prepared from at least one aliphaticuretdione polyisocyanate (especially cycloaliphatic uretdionepolyisocyanate), preferably from at least 20 mol % aliphatic uretdionepolyisocyanate based on the total amount of polyisocyanates used,particularly preferred only from aliphatic uretdione polyisocyanates.

The uretdione polyisocyanate A1 is used in an amount of 3 to 50 wt.-%based on the total amount of reactants used for preparation of saiduretdione prepolymer.

The sum of compounds A2 and A3 is preferably used in an amount of 50 to97 wt.-% based on the total amount of reactants used for preparation ofsaid uretdione prepolymer.

For preparation of said uretdione prepolymer it is particularlypreferred to use the uretdione polyisocyanate A1 in relation to saidcompound A2 in a weight ratio from 1:1 to 1:32.3.

Most preferably, compound A2 is used in a total amount of 1 to 25 wt.-%,preferably 5 to 20 wt.-% and compound A3 is used in a total amount of 20to 70 wt.-%, preferably 35 to 65 wt.-%, based on the total amount ofreactants used for preparation of said uretdione prepolymer.

The aqueous, curable composition preferably comprises less organicsolvents compared to conventional curing compositions. According to theinvention, water is used in the composition as a component (preferablyas the main component) of the liquid continuous phase of the dispersion.Replacement of organic solvents, especially of low-VOC compounds, bywater leads to more ecologically friendly compositions. Preferredcompositions according to the invention are characterized in that theycomprise water preferably in an amount of 10 to 85 wt. %, particularlypreferred in an amount of 30 to 75 wt. %, most preferred in an amount of50 to 70 wt. %, also preferred in an amount from 40 to 70 wt. %, mostpreferred in an amount of 60 to 70 wt. %, based on the total weight ofthe composition respectively.

The aqueous, curable compositions of the invention have a preferredpH-value at 20° C. of from pH 5 to pH 13, more preferred from pH 6 to pH12, even more preferred from pH 7 to pH 9.

In order to further improve the physiological compatibility, thecomposition of the invention is preferably substantially free ofcompounds comprising at least one isocyanate group. Due to the waterpresent in the composition, the majority up to all isocyanate groupswill hydrolyze. Preferably the content of the isocyanate groups(expressed as NCO, M.G. 42 g/mol) is below 0.05 wt.-%. Particularlypreferred, the composition of the invention is free of compoundscomprising at least one isocyanate moiety. Unless expressly mentionedotherwise, NCO contents were determined volumetrically in accordancewith DIN-EN ISO 11909 (the DIN-version used at the application date (orat the priority date if applicable) of the present invention at thelatest version).

In a preferred embodiment, the composition comprises said uretdioneprepolymer in a total amount of 1 to 50 wt. %, preferably 3 to 40 wt. %and most preferred 30 to 40 wt. %, based on the weight of the totalcomposition.

Preferred compositions of this embodiment of the invention comprise atleast one Zerewitinoff-active compound. Suitable compounds are thecompounds as disclosed above for A2 and A3. Preferred compound areselected from polyester polyol, polyether polyol, polycarbonate polyol,polyurethane polyol, polyacrylate polyol, polymethacrylate polyol,C₂-C₁₀-hydrocarbon with at least two hydroxyl groups, or mixturesthereof.

The aqueous, curable composition of this invention preferably comprisesat least one azolate-compound. According to theHantzsch-Widman-nomenclature (IUPAC-rule RB-1.2, R-2.3.3.1) an azole isthe generic term for unsaturated five-membered heterocyclic compounds,comprising in the cycle one nitrogen atom and in addition to thatoptionally at least one or more further hetero atoms including nitrogenatom. An azolate-compound according to this invention comprises anazole-anion (azolate).

Preferred azolate compound comprise a five-membered N-heterocycle. Thering of said preferred N-heterocycle contains an amount of n nitrogenatoms with n=1, 2 or 3 and an amount of (5-n) carbon atoms. In additionto that, the five membered ring of said N-heterocycle comprises twoendocyclic double bonds. Said endocyclic double bonds are preferablyconjugated double bonds. The five-membered N-heterocycle is negativelycharged. Said negative charge is delocalized. Preferably, the endocyclicdouble bonds contribute to the delocalization of the negative charge.

Preferred compositions comprise at least one azolate-compound of formula(II)

wherein

one, two or three moieties of X¹, X², X³ and X⁴ independently of oneanother represent the moiety “—N═” wherein the rest of the moieties ofX¹, X², X³ and X⁴ independently of one another represent “—CR═”, whereinR independently represents H, C₁ to C₂₀ alkyl, C₃ to C₂₀ cycloalkyl C₆to C₂₀ aryl, C₁ to C₂ alkoxy, —NR′₂ (R′═C₁ to C₂₀ alkyl), —NO₂,fluorine, chlorine, bromine, fluorinated C₁-C₆-alkyl, fluorinatedC₁-C₆-alkoxy, cyano, carboalkoxy, —S—R″ (R″═C₁ to C₂₀ alkyl), and/or—S—(C₆ to C₂₀ aryl) and in the event two adjacent subsitutents of X¹ toX⁴ represent “—CR═”, the substituents R of these substituents togetherwith the C-atoms of these substituents may form a further annellatedcarbo- or heterocyclic, n-membered ring system where n=3 to 10, whereinthe annellated carbo- or heterocyclic ring system may, independently ofone another, contain one or more heteroatoms (N, 0, S) and may besubstituted independently of one another by one or more the same ordifferent substituents from the following group: H, C₁ to C₂₀ alkyl, C₃to C₂₀ cycloalkyl C₆ to C₂₀ aryl, C₁ to C₂ alkoxy, —NR′₂ (R′═C₁ to C₂₀alkyl), —NO₂, fluorine, chlorine, bromine, fluorinated C₁-C₆-alkyl,fluorinated C₁-C₆-alkoxy, cyano, carboalkoxy, —S—R″ (R″═C₁ to C₂₀alkyl), and/or —S—(C₆ to C₂₀ aryl), Cat⁺ is a counterion.

The cycle of formula (II) represents a 7c-system, comprising the twoendocyclic double bonds and the delocalized charge.

The azolate compounds are usually prepared by deprotonation of a neutralazole compound. Deprotonation is achieved preferably with a base,preferably with alkaline alkoxides like sodium methanolate, alkalineearth alkoxides, alkaline hydroxides or alkaline earth hydroxides. Theazolate compound of formula (II) is prepared by deprotonization ofneutral compounds of formula (II-1) with a base, preferably with atleast one of the above mentioned preferred bases,

wherein X¹, X², X³ and X⁴ are defined according to formula (II).

Other suitable neutral compounds for preparation of the azolate compoundaccording to the invention include pyrrole, substituted pyrroles andcarbocyclic and/or heterocyclic annellated derivatives of pyrrole.

Other suitable neutral compounds for preparation of the azolate compoundaccording to the invention include pyrazole and/or imidazole,substituted pyrazoles and/or imidazoles and carbocyclically and/orheterocyclically annellated derivatives of pyrazole and/or imidazole.

Other suitable neutral compounds for preparation of the azolate compoundaccording to the invention include triazole, preferably selected from1,2,3- and 1,2,4-triazoles, substituted species of 1,2,3- and1,2,4-triazoles and carbocyclically and/or heterocyclically annellatedspecies of 1,2,3- and 1,2,4-triazoles.

To produce the azolate compound, in principle all five-memberedN-heterocycles may be used which carry at least one hydrogen atom boundto a ring nitrogen atom. Examples of these include pyrrole, indole,carbazole and substituted derivatives such as 5-nitroindole or5-methoxyindole, pyrazole, indazole and substituted derivatives such as5-nitroindazole, imidazole and substituted derivatives such as4-nitroimidazole or 4-methoxyimidazole, benzimidazole or substitutedbenzimidazoles, for example 5-nitrobenzimidazole,5-methoxybenzimidazole, 2-trifluoromethylbenzimidazole, hetero-aromaticannellated imidazoles such as pyridinoimidazole or purine,1,2,3-triazole and substituted derivatives such as4-chloro-5-carbomethoxy-1,2,3-triazole or4-chloro-5-cyano-1,2,3-triazole, 1,2,4-triazole and substitutedderivatives such as 3,5-dibromotriazole, 1,2,3-benzotriazole andsubstituted 1,2,3-benzotriazole such as 5-fluor-1,2,3-benzotriazole,5-trifluoromethyl-1,2,3-benzotriazole, 5-nitro-1,2,3-benzotriazole,5-methoxy-1,2,3,-benzotriazole, 5-chloro-1,2,3-benzotriazole,5-tetrafluoroethoxy-1,2,3-benzotriazole,5-trifluorothio-1,2,3-benzotriazole,4,6-bis-(trifluoromethyl)-1,2,3-benzotriaole,4-trifluoromethoxy-5-chloro-1,2,3-benzotriazole and heteroaromaticannellated 1,2,3-triazoles such as the isomeric pyridinotriazoles, forexample the 1H-1,2,3-triazolo[4,5-b]pyridine—referred to in theremainder of the text as pyridinotriazole- and azapurine.

In particularly preferred compositions of the invention, the compositioncomprises at least one triazolate-compound as component C).

Said triazolate-compound is most preferably selected from at least onetriazolate-compound of formula (III) or their corresponding salts andformula (IV) or their corresponding salts

wherein

R¹, R², R³ and R⁴ independent from one another denote a hydrogen atom, ahalogen atom, a nitro group, a saturated or unsaturated, aliphatic orcycloaliphatic radical, an optionally substituted aromatic groupcomprising up to 20 carbon atoms and optionally up to 3 heteroatomsselected from oxygen, sulphur, nitrogen, an optionally substitutedaraliphatic group comprising up to 20 carbon atoms and optionally up to3 heteroatoms selected from oxygen, sulphur, nitrogen, and where R³ andR⁴ of formula (IV) together with the carbon atoms of the1,2,3-triazolate five-membered ring form fused rings with 3 to 6 carbonatoms.

Said triazolate-compound is particularly preferred selected fromalkaline metal-1,2,4-triazolate, alkaline metal-1,2,3-triazolate,alkaline metal-benzotriazolate, alkaline earth metal-1,2,4-triazolate,alkaline earth metal-1,2,3-triazolate, alkaline earthmetal-benzotriazolate. Especially preferred, the triazolate-compound isselected from alkaline metal-1,2,4-triazolate, alkalinemetal-1,2,3-triazolate, alkaline metal-benzotriazolate. Sodium1,2,4-triazolate, potassium 1,2,4-triazolate, sodium 1,2,3-triazolate,potassium 1,2,3-triazolate, sodium benzotriazolate, potassiumbenzotriazolate and mixtures thereof are the most preferredtriazolate-compounds.

It was proven advantageous to preferably apply curable compositions,which comprise said azolate-compound, preferably saidtriazolate-compound, in an amount of 0.1 to 10.0 wt. %, particularlypreferred of 0.3 to 3 wt. %, based on the weight of the compositionrespectively. Particularly preferred curable compositions of theinvention comprise said uretdione prepolymer in an amount of 1 to 50 wt.%, preferably 3 to 40 wt. % and most preferred 30 to 40 wt. % and saidazolate-compound, preferably said triazolate-compound, in an amount of0.1 to 10.0 wt. %, preferably 0.3 to 3 wt.-%, based on the weight of thecomposition respectively.

In addition to the ingredients mentioned the composition above maycontain various optional ingredients. Examples of these are dyes,pigments, fillers and reinforcing agents, for example calcium carbonate,silicates, talc, kaolin, mica and barium sulfate. Other additives, forexample plasticizers, lubricants and rheological additives and solventor diluent may be included in the compositions. When present, theseoptional ingredients may constitute up to 50% by weight of thecomposition based on total weight of the composition.

Of particular interest is the use of the compositions of the inventionfor preparing coatings on substrates of all kinds. Such coatings arepreferably protective and decorative coatings such as exterior coatingson substrates of all kinds, for example buildings, fences, chipboardpanels, and as a coating on stone, concrete or metal, for the coating ofvehicles, for example, such as cars, railways or aircraft. Thecompositions may likewise be used in automotive OEM finishing andautomotive refinish, and also for the finishing of car bodies, plasticparts for cars and body-mounted car parts.

The compositions of the invention can also be used as sealants oradhesives.

Furthermore, the present invention pertains to a process for curing aliquid composition on a substrate, comprising

a) applying on a substrate an aqueous, curable composition according tothe present invention; and

b) exposing the deposited aqueous, curable composition to a temperatureof 60° C. to 160° C. to cure said deposited curing composition.

Using known coating processes, the aqueous, curable composition may beapplied uniformly to a substrate, for example by spin coating, dipcoating, knife coating, curtain coating, brushing, spraying—especiallyelectrostatic spraying—and reverse roll coating. Said coatingcompositions can be used as a primer, color coat or as a clear coat.

The previously described preferred embodiments of said aqueous, curablecomposition are of course also preferably used in the process of thisinvention.

The choice of diluent and the concentration depend predominantly on thechoice of coating ingredients and the coating process. The diluentshould preferably be inert. In other words, it should not undergo anychemical reaction with the components and should be capable of beingremoved after the coating operation in the curing process. Surprisinglyit was found, that especially water is an appropriate diluent. Examplesof suitable diluents are water, ketones, ethers and esters, such asmethyl ethyl ketone, isobutyl methyl ketone, cyclopentanone,cyclohexanone, N-methylpyrrolidone, dioxane, tetrahydrofuran,2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol,1,2-dimethoxyethane, ethyl acetate, n-butyl acetate and ethyl3-ethoxypropionate. It is particularly preferred to use water asdiluent.

It is particularly preferred, that the deposited aqueous curablecomposition coalesces to form a coating. The coating thickness upondrying is typically from 0.5 to 46 μm. If the coating is a base coat,the coating thickness upon drying is preferably 15 to 20 μm. If thecoating is a top coat, the coating thickness upon drying is preferably45 to 50 μm.

The deposited aqueous, curable composition is preferably exposed to atemperature of 60 to 120° C., preferably 80 to 100° C., to cure saiddeposited curing composition.

According to the process of the invention, the deposited aqueous,curable composition is preferably exposed to said temperature for aperiod of 20 to 45 minutes to cure said deposited curing composition. Itis particularly preferred to expose the deposited aqueous, curablecomposition to a temperature of 60 to 120° C., preferably 80 to 100° C.,for a period of 20 to 45 minutes.

It is also preferred to cure said deposited, aqueous curable compositionby preheating the deposited, curable composition to a temperature of 30°C. to below 60° C. for a period of 2 to 10 minutes. Said preheating isparticularly preferred followed by increasing the temperature to 60 to160° C. (preferably to 60 to 120° C., most preferred to 80 to 100° C.)and exposing for another period of 20 to 45 minutes at said increasedtemperature. The preheating step is advantageous, since the amount ofwater is reduced in the deposited, curable composition prior to curing.The subsequent curing reaction at 60° C. to 160° C. is thereby enhanced.

Preferably, the cured aqueous curable composition forms a crosslinkedfilm on the substrate, preferably forms a transparent solid on thesubstrate, that shows excellent mechanical and optical properties and ahigh resistance against chemicals and solvents.

EXAMPLES

Compounds:

Ymer N120 (CAS number: 131483-27-7), a linear, trimethylolpropanestarted polyethylene glycol monomethyl ether, OH number 100-120 mgKOH/g) was acquired from Perstorp Holding AB, Malmö, Sweden.

Polyester 1 OH-functional polyester prepared from 3039 g adipic acid,4041 g isopthalic acid, 267 g 1,2-propylene glycol, 4773 g neopentylglycol and 1419 g trimethylol propane (OH number: 181 mg KOH/g, acidnumber<3 mg KOH/g)

Other chemicals were—unless otherwise stated—purchased at Sigma-AldrichChemie GmbH, Munich, Germany

-   -   IPDI uretdione (“IPDI-dimer”): To 1000 g (4.50 mol) of        isophorone diisocyanate (IPDI) were added at room temperature        under dry nitrogen and stirring 10 g (1%) of triisodecyl        phosphite and 20 g (2%) of 4-dimethylaminopyridine (DMAP) as        catalyst. After 20 h, the reaction mixture, which had an NCO        content of 28.7%, corresponding to a degree of oligomerization        of 21.8%, was freed from volatile components without prior        addition of a catalyst poison with the aid of a thin-film        evaporator at a temperature of 160° C. and a pressure of 0.3        mbar.        -   This gave a pale yellow uretdione with a content of free NCO            groups of 17.0%, a content of monomeric IPDI of 0.4% and a            viscosity (according to DIN EN ISO 3219: 1994-10) of more            than 200,000 mPas (23° C.).

Measurement Methods:

Unless noted otherwise, all of the analytical measurements refer tomeasurements at temperatures of 23° C.

All percentages refer, unless otherwise stated, to the weight.

The solids contents (non-volatile contents) were determined by heating aweighed sample (approx. 1 g) at 105° C. to constant weight. At constantweight, the solid-body content is calculated by reweighing the sample.

The pendulum hardness by the König method was measured on a glass plateaccording to DIN EN ISO 1522:2007-04.

NCO contents were determined volumetrically in accordance with DIN-ENISO 11909:2007-05. The control on free NCO groups was carried out bymeans of IR spectroscopy (band at 2260 cm⁻¹).

The stated viscosities were determined by means of rotary viscometry inaccordance with DIN 53019:2008-09 at 23° C. using a rotary viscometerwith a shear rate of 186 l/s, from Anton Paar Germany GmbH, Ostfildern,Germany.

The average particle sizes (the number-average is given) of thepolyurethane dispersions were determined following dilution withdeionized water by means of laser correlation spectroscopy (instrument:Malvern Zetasizer 1000, Malver Inst. Limited, London, UK).

Zeta potential was measured by diluting one drop of the sample with 20ml demineralized water and homogenized by stirring. Subsequently thezeta potential is determined at 23° C. in the Malvern Nanosizer ZS90″(Malvern Instruments, Herrenberg, Germany).

Acid number of the respective dispersion was determined according to DINISO 2114 1:2006-11. Instead of a mixture of toluene and ethanol—asdescribed in DIN ISO 2114 1:2006-11—a mixture of acetone and ethanol(2:1 by weight) was used as solvent. The unit of the acid number is mgKOH per g of the analyzed sample.

Solvent Resistance and Water Resistance:

The cured coating films were tested for their resistance to xylene andwater. A piece of cotton wool soaked with the test substance was placedon the coating surface and covered with a watch glass. After thespecified exposure time, the cotton wool was removed; the exposed sitewas dried and immediately inspected. The evaluation of the softening ordiscoloring of the coating surface was carried out following the DIN ENISO 4628-1:2016-07:

0: unchanged, i.e. no perceptible change

1: very slight, i.e. barely perceptible change

2: slight, i.e. clearly perceptible change

3: moderate, i.e. very clearly perceptible change

4: considerable, i.e. pronounced change

5: very marked change

Infrared Measurements:

The uretdione ring opening was characterized by an FT-IR spectrometer(tensor II with Platinum ATR unit (diamond crystal) from Bruker). Thespectra were recorded in a wave number range of (4000-400) cm⁻¹. Themaximum of the uretdione peak (about 1760 cm ⁻¹) was evaluated. Peakheights to comparative systems were compared with an initial value setto 100% (uretdione film without catalyst, dried at room temperature) andvariations relative to this (ratio formation). Uretdione peak height offilms cured for 30 min at 180° C. were set to 0%. When measuring on anATR crystal, the intensity of the spectrum depends on the occupation ofthe crystal surface. Since a comparable coverage of the crystal surfacecannot be ensured in the case of different measurements by the samplepreparation, a correction of this effect must be made for the ratioformation by normalizing all spectra on the peak of the CH stretchingvibration (wave number range (3000-2800 cm⁻¹). In the case of theevaluation of peak heights as described above, a baseline correction ofthe spectra is additionally carried out.

Preparation of Uretdione Prepolymer Dispersion A (According to theInvention)

149.0 g of “IPDI uretdione” were dissolved in 580 g acetone at 50° C. ina standard stirring apparatus. 64.6 g of Ymer N120 and 0.53 g of tinneodecanoate were added and the mixture was stirred at reflux underatmospheric pressure until the NCO content of 2.5% was reached. Then213.2 g of polyester 1 were added and the mixture was stirred underreflux at atmospheric pressure until the NCO content dropped below 0.5%.The mixture was then dispersed by adding 213.2 g of water. The solventwas removed by distillation in vacuum; solid content was adjusted byaddition of water.

The resulting white dispersion had the following properties:

Solids content: 37%

Average particle size (LCS): 107 nm

Viscosity (viscometer, 23° C.): 118 mPas

pH (23° C.): 5.3

Acid number: 0.9 mg KOH/g

Zeta potential: −16.4 mV

Comparative Dispersion 1

149.1 g of “IPDI-dimer” were dissolved in 580 g acetone at 50° C. in astandard stirring apparatus. 63.4 g of Poly(ethylene glycol) methylether with an average Mn of 500 g/mol, 214.24 g of a OH-functionalpolyester 1 and 0.53 g of tin neodecanoate were added and the mixturewas stirred at reflux under atmospheric pressure until the NCO contentdropped below 0.5%. Then 794 g of water were added. The acetone wasremoved by distillation in vacuum; solid content was adjusted byaddition of water.

The resulting white dispersion had the following properties:

Solids content: 35.7%

Average particle size (LCS): 166 nm

Viscosity (viscometer, 23° C.): 20 mPas

pH (23° C.): 5.4

Preparation of Anionic Uretdione Prepolymer Dispersion (ComparativeExample) Comparative Dispersion 2

150.3 g of “IPDI-dimer” were dissolved in 594 g acetone at 50° C. in astandard stirring apparatus. 12.8 g of dimethylol propionic acid, 201.3g of a OH-functional polyester 1 and 0.55 g of tin neodecanoate wereadded and the mixture was stirred at reflux under atmospheric pressureuntil the NCO content dropped below 0.5%. Then 8.5 gN,N-dimethylamino-ethanol and 670 g of water were added. The acetone wasremoved by distillation in vacuum; solid content was adjusted byaddition of water.

The resulting white dispersion had the following properties:

Solids content: 35.6%

Average particle size (LCS):108 nm

Viscosity (viscometer, 23° C.): 5 mPas

pH (23° C.): 8.5

Acid number: 7.3 mg KOH/g

Zeta potential: −45.7 mV

Tests of the Coatings

Clear coatings were prepared from the following composition:

100 weight percent (20 g) of urethane prepolymer dispersion A (orcomparative) was mixed with 6 weight percent (1.2 g) of a solutionconsisting of 0.12 g 1,2,4-Triazolate-Na and 1.08 g water.

The mixture was applied to glass or coil (CS-300570 coil coating testpanel, purchased from Zanders PBL) using a coating squeegee with a layerthickness of 150-180 μm (wet). The plates were dried at room temperaturefor 5 minutes and then baked at various temperatures for 30 minutes. Theobtained films were evaluated at 23° C. at 50% relative humidity bypendulum hardness, water resistance and solvent resistance and an IRspectrum was recorded.

The following table shows the coating properties of the correspondingfilms.

Requirements for Coatings:

Pendulum hardness>100 s

Xylene test:<4

10 weeks stable at room temperature and 40° C.

Inventive Examples Ex1 (with Catalyst) and Ex 2 (without Catalyst)

Clear Coat of the Following Compositions:

Ex 1 Ex 2 Dispersion A 20 g 20 g Catalyst 1,2,4-Triazolate-Na 1.2 g (10%in water)

Coating Properties (Before Storage):

Ex 1 Ex 2 Curing Time, 1 day; 1 day; Temperature room temp. room temp.Remaining intensity of IR- Percent >97% >97% peak with peak maximumbetween 1750 and 1800 cm⁻¹ Resistance against xylene 5 min 5 5 Ex 1 Ex 2Curing Time, 30 min; 30 min; Temperature 100° C. 100° C. Remainingintensity of IR- Percent <3% >97% peak with peak maximum between 1750and 1800 cm⁻¹ Resistance against xylene 5 min 2 5 Ex 1 Ex 2 Curing Time,30 min; 30 min; Temperature 140° C. 140° C. Remaining intensity of IR-Percent <3% 92% peak with peak maximum between 1750 and 1800 cm⁻¹Resistance against xylene 5 min 2 5

Coating Properties of Inventive Dispersion (Ex 1) which were StoredBeforehand at Room Temperature and at 40° C.:

20 g stored at 20 g stored at room temperature 40° C. Ex 1 for 10 weeksfor 10 weeks Curing Time, 30 min; 30 min; Temperature 100° C. 100° C.Remaining intensity of IR- Percent <3 <3 peak with peak maximum between1750 and 1800 cm⁻¹ Resistance against xylene 5 min 2-3 2-3

Comparative Examples 1 and 2: Comparative Dispersion 1

Clearcoat of the Following Compositions:

Comp. Ex 1 Comp. Ex 2 Comp. Dispersion 1 20 g 20 g Catalyst1,2,4-Triazolate-Na 1.2 g (10% in water)

Coating Properties (Before Storage):

Comp. Ex 1 Comp. Ex 2 Curing Time, 30 min; 30 min; Temperature 100° C.100° C. Remaining intensity of IR- Percent <3% >97% peak with peakmaximum between 1750 and 1800 cm⁻¹ Resistance against xylene 5 min 4 5Comp. Ex 1 Comp. Ex 2 Curing Time, 30 min; 30 min; Temperature 140° C.140° C. Remaining intensity of IR- Percent <3% >97% peak with peakmaximum between 1750 and 1800 cm⁻¹ Resistance against xylene 5 min 4 5

Comparative Examples 3 and 4: Comparative Dispersion 2

Clearcoat of the Following Compositions:

Comp. Ex 3 Comp. Ex 4 Comparative Dispersion 2 20 g 20 g Catalyst1,2,4-Triazolate-Na 1.1 g (10 wt.-% in water)

Coating Properties (Before Storage):

Comp. Ex 3 Comp. Ex 4 Curing Time, 30 min; 30 min; Temperature 100° C.100° C. Remaining intensity of IR- Percent >97 >97 peak with peakmaximum between 1750 and 1800 cm⁻¹ Resistance against xylene 5 min 5 5Comp. Ex 3 Comp. Ex 4 Curing Time, 30 min; 30 min; Temperature 140° C.140° C. Remaining intensity of IR- Percent >97 >97 peak with peakmaximum between 1750 and 1800 cm⁻¹ Resistance against xylene 5 min 4 4

Coating properties of non-inventive dispersions after storage at 40° C.or with catalyst could not be performed due to instability of thesedispersions.

Stability Measurements of Examples and Comparative Example 1:

Dispersions were stored at room temperature or in a 40° C. oven with orwithout catalyst for 10 weeks. Stability of dispersion was evaluated byIR measurement before/after storage.

Inventive Comparative Dispersion Example A dispersion 1 Remainingintensity of IR-peak >97% Thickened after after storage at roomtemperature storage at RT without catalyst for 10 weeks for 8 weeks(peak maximum between 1750 and 1800 cm⁻¹) Remaining intensity ofIR-peak >86% Thickened after storage at 40° C. without catalyst for 10weeks (peak maximum between 1750 and 1800 cm⁻¹) Remaining intensity ofIR-peak 87 Thickened after storage at room temperature with catalyst for10 weeks (peak maximum between 1750 and 1800 cm⁻¹) Remaining intensityof IR-peak  44% Thickened after storage at 40° C. with catalyst for 10weeks (peak maximum between 1750 and 1800 cm⁻¹)

1. A uretdione prepolymer, which comprises at least one uretdione group,and which is obtained by reacting A1) at least one uretdionepolyisocyanate having an isocyanate functionality of at least 2.0,wherein said uretdione polyisocyanate is obtained from at least onealiphatic polyisocyanate, with A2) at least one polyalkoxy etherderivative comprising at least two —OH groups, which are present on twodifferent non neighboring atoms of the molecule and wherein at least oneof the —OH groups is not a terminal —OH group, and A3) at least onereactant, which comprises at least one Zerewitinoff-active group andbeing different from A2 or which is H₂O, in the presence of at least onecatalyst, to obtain the uretdione prepolymer, wherein the prepolymer hasan acid number of at most 4 mg KOH/g.
 2. The uretdione prepolymeraccording to claim 1, wherein in a first step, the at least oneuretdione polyisocyanate A1 is reacted, with the at least one polyalkoxyether derivative A2 and in a second step the polymer obtained in thefirst step is reacted with the at least one reactant A3.
 3. Theuretdione prepolymer according to claim 1, wherein components A1 to A3are reacted in a one-step process.
 4. The uretdione prepolymer accordingto claim 1, wherein in a first step, the at least one uretdionepolyisocyanate A1 is reacted with the at least one reactant A3 and in asecond step the polymer obtained in the first step is reacted in asecond step with the at least one polyalkoxy ether derivative A2.
 5. Theuretdione prepolymer according to claim 1, where-in said uretdioneprepolymer is a nonionic prepolymer.
 6. The uretdione prepolymeraccording to claim 1, wherein said uretdione prepolymer exhibits a zetapotential of at least −20 mV.
 7. The uretdione prepolymer according toclaim 1, wherein said uretdione polyisocyanate A1 is obtained from atleast one cycloaliphatic polyisocyanate.
 8. The uretdione prepolymeraccording to claim 1, wherein said uretdione polyisocyanate A1 isprepared from isophorone diisocyanate as the only polyisocyanate.
 9. Theuretdione prepolymer according to claim 1, wherein compound A2 isselected from compounds of formula (I):

wherein, X is H or alkyl; R is a C₁₋₄ alkylene group; p is an integer of2 to 50; in each unit p n is independently 0 or 1 and m is independently0 or 1, with the proviso that at least one of n or m in each unit pis
 1. 10. The uretdione prepolymer according to claim 1, whereincompound A3 is selected from the group consisting of at least onepolyol, which is different from A2, from polyester polyols, polyetherpolyols, polyurethane polyols, polyacrylate polyols, polymethacrylatepolyols, polycarbonate polyols, and mixtures thereof.
 11. An aqueous,curable composition, comprising: the uretdione prepolymer according toclaim 1, and optionally, at least one compound, which comprises at leastone Zerewitinoff-active group and/or optionally, at least oneazolate-compound.
 12. The aqueous, curable composition according toclaim 11, wherein said uretdione prepolymer is contained in a totalamount of 3 to 40 wt. %, based on the total weight of the composition.13. The aqueous, curable composition according to claim 11, wherein saidazolate-compound is selected from the group consisting of at least onetriazolate-compound of formula (III) or salts thereof and formula (IV)or salts thereof

wherein, R¹, R², R³ and R⁴ are independently selected from a hydrogenatom, a halogen atom, a nitro group, a saturated or unsaturated,aliphatic or cycloaliphatic radical, an optionally substituted aromaticgroup comprising up to 20 carbon atoms and optionally, up to 3heteroatoms selected from oxygen, sulfur, and nitrogen, an optionallysubstituted araliphatic group comprising up to 20 carbon atoms andoptionally, up to 3 heteroatoms selected from oxygen, sulfur, andnitrogen, and wherein R³ and R⁴ of formula (IV) together with the carbonatoms of the 1,2,3-triazolate five-membered ring form fused rings with 3to 6 carbon atoms.
 14. The aqueous, curable composition according toclaim 13, wherein said azolate-compound is selected from the groupconsisting of alkaline metal-1,2,4-triazolate, alkalinemetal-1,2,3-triazolate, alkaline metal-benzotriazolate, alkaline earthmetal-1,2,4-triazolate, alkaline earth metal-1,2,3-triazolate, andalkaline earth metal-benzotriazolate.
 15. The aqueous, curablecomposition according to claim 11, wherein said at least one compound,which comprises at least one Zerewitinoff-active group is selected fromthe group consisting of polyester polyols, polyether polyols,polyurethane polyols, polyacrylate polyols, polymethacrylate polyols,polycarbonate polyols, and mixtures thereof.
 16. The aqueous, curablecomposition according to claim 11, wherein said uretdione prepolymer iscontained in an amount of 1 to 50 wt. % or said at least one compound,which comprises at least one Zerewitinoff-active group is contained inan amount of 0 to 80 wt.-% or said triazolate-compound is contained inan amount of 0.1 to 10 wt. %, based on the total weight of thecomposition, respectively.
 17. A process for curing a liquid compositionon a substrate, comprising a) applying on a substrate an aqueous,curable composition according to claim 11; and a) exposing the aqueous,curable composition to a temperature of 60° C. to 160° C. to cure saidcomposition.
 18. The cured article obtained by the process according toclaim
 17. 19. In a process for the production of one of a coating, anadhesive and a sealant, the improvement comprising including thecomposition according to claim 11.